1. Field of the Invention
The present invention relates to mobile phones and, more particularly, to a mobile phone having an image projection function.
2. Description of the Related Art
In recent years, portable terminal devices such as mobile phones that are equipped with an image projection device (projector) have been developed.
For example, Japanese Patent Application Publication No. Hei 2-184886 discloses a portable terminal device as shown in FIG. 12. This portable terminal device has a terminal device body 61, a keypad 62, a transmissive liquid crystal panel 63 that forms an image for projection, a light source 64 for image projection, and a control unit 65. In this device, the control unit 65 is operated through the keypad 62 to form an image on the transmissive liquid crystal panel 63 according to a control signal from the control unit 65, and light P from the light source 64 passing through the transmissive liquid crystal panel 63 is projected on a screen 100.
Japanese Patent Application Publication No. 2004-317871 discloses a mobile phone as shown in FIG. 13. This mobile phone has a transmissive liquid crystal panel 73 and a projection lamp 74 that are pivotally attached to a mobile phone body 71 through respective pivot shafts 73a and 74a. An image that is formed on the transmissive liquid crystal panel 73 according to a control signal from a control unit 75 is projected on a screen 100 by light from the projection lamp 74.
The above-described portable terminal device and mobile phone, however, have no lens for projection. Therefore, the projected image can appear sharp only on the screen placed in close proximity to the transmissive liquid crystal panel. Thus, a sufficient magnified image projection function cannot be attained.
Accordingly, it is practically necessary to provide a projection lens in front of the transmissive liquid crystal panel.
FIG. 14 shows a projection lens 88 provided in front of a transmissive liquid crystal panel 83 that is illuminated by a light source 84 for image projection. If the projection lens 88 is larger in shape than the transmissive liquid crystal panel 83 as shown in part (a) of FIG. 14, both image light P1 from the vicinity of the center G1 of the transmissive liquid crystal panel 83 and image light P2 from the vicinity of a peripheral edge point G2 of the transmissive liquid crystal panel 83 pass through the projection lens 88 and are imaged on the screen 100.
In contrast, if the projection lens 88 is smaller in shape than the transmissive liquid crystal panel 83, as shown in part (b) of FIG. 14, all the image light P2 from the peripheral edge point G2 of the transmissive liquid crystal panel 83 cannot pass through the projection lens 88, but only a part P2a (hatched portion) thereof passes through the projection lens 88 and is imaged on the screen 100.
Accordingly, when the projection lens 88 is smaller than the transmissive liquid crystal panel 83, the image formed on the screen 100 is darker than when the projection lens 88 is larger than the transmissive liquid crystal panel 83. Therefore, it is preferable to use a projection lens larger in shape than a transmissive liquid crystal panel on which an image to be projected is formed.
In general, however, a liquid crystal panel for information display used in a mobile phone is maximized to nearly the size of the external shape of the mobile phone body in a display part of the mobile phone. Therefore, if a projection lens larger than the liquid crystal panel is installed in the mobile phone, the size of the mobile phone unavoidably needs to be increased, which will impair the portability of the mobile phone.